The present invention relates to a method of and an apparatus for recording an image, and more particularly to a method of and an apparatus for thermally recording an image, characters, or the like on a heat sensitive recording material with a thermal head, such that an image having a large blackened area can be reproduced with a high image quality, using a heat sensitive recording material which comprises a support coated with a coating solution that makes a thermally recorded area transparent and the other area black.
Various new medical image diagnostic apparatus such as ultrasonic imaging apparatus, X-ray computerized tomographic apparatus, and nuclear magnetic resonance imaging apparatus have recently been widely used in addition to conventional X-ray photographic apparatus in the medical field. In such medical image diagnostic apparatus, an ultrasonic beam or X-ray is applied to the body of a patient, and any change in the utrasonic or X-ray energy that has passed through or been reflected from the patient's body is detected. Based on the detected change image information of a localized region in the patient's body is produced. The image information is then displayed on a CRT monitor, for example. A doctor is required to diagnose the localized region of the patient's body by looking at the image displayed on the CRT monitor. Other localized regions of the patient's body can also be easily observed in the same manner as described above when it is desired to do so. Therefore, the diagnostic process can be carried out accurately and quickly.
It is sometimes necessary for the doctor to send monitored images to other hospitals or to look at time-dependent changes of localized regions together with patients. In view of this, it has been desired to record monitored images permanently on recording mediums. Various image recording apparatus have been developed and used to meet such a demand. Such image recording apparatus include a multiformat camera for recording images displayed on a CRT monitor or a photosensitive material through an optical system, and a laser beam printer for modulating the intensity of a light beam with a video signal representing an image displayed on a CRT monitor and recording the image on a photosensitive recording material with the intensity-modulated light beam.
These image recording apparatus are however large in size since they comprise a CRT monitor, a light detector, etc., and an optical system including these devices occupy a large space in the apparatus. If such an image recording apparatus is used for a medical application, it must be combined with an automatic developing machine which can rapidly produce a photographic film with a fixed image thereon for immediate medical diagnosis. The image recording apparatus and the automatic developing machine associated therewith are much larger in size.
Materials such as photographic films used for medical diagnosis are legally required to be kept as records for a certain period of time. Therefore, hospitals and other medical institutions must have a considerably large space for keeping such records, and the space available in these organizations should be efficiently utilized. The large size image recording apparatus however do not meet the requirement for such efficient space utilization.
Heat sensitive recording processes employing heat sensitive materials for thermally recording images thereon are finding wide use in facsimile receivers and printers since the processes are easy to perform, the apparatus used are simple in structure and inexpensive to manufacture.
Photographic films on which images of localized regions of patent's bodies are recorded based on video signals produced by X-ray photographic apparatus, ultrasonic imaging apparatus, X-ray computerized tomographic apparatus, and nuclear magnetic resonance imaging apparatus are observed by doctors for medical diagnosis of the imaged localized regions while these films are being placed on a light table such as an illuminating box. An image thermally recorded on a film using a thermal head has a large blackened area so that the eyes of the observer will not be glared by any reflected light from the film, as shown in FIG. 1 of the accompanying drawings.
When a film 2 (FIG. 1) paced on a light table is observed, the intensity of light passing through a non-image area 6 on the peripheral portion of the film which is not blackened is larger as compared with an image area 4 where the image is thermally recorded. Therefore, the image area 4 which contains necessary information for the doctor may not be clearly visually recognized. The conventional heat sensitive recording mediums make thermally recorded areas black. Therefore, the thermal head for recording images is heated almost at all times. To prevent the apparatus from increasing its temperature excessively, a heat radiating fan and large-size heat radiating fins for allowing active components to operate reliably are required by the apparatus, with the result that the apparatus become large in size. When medical images are successively recorded using a thermal head, the heat stored in the thermal head is greatly increased, and it becomes highly difficult to produce images of stable densities.
Under the circumstances, there has been a demand for a heat sensitive material in which only an area recorded by a thermal head is made transparent and the other background area is of a high-density color such as black, so that the developed image on the heat sensitive material can be viewed on a light table or an overhead projector.
To meet such a demand, a heat sensitive recording material has been developed as disclosed in Japanese Pat. application No. 62-60646 filed by the applicant. The disclosed heat sensitive recording material is produced by coating on a support and drying a coating composition containing an emulsion prepared by dissolving a colorless or light colored electron-donating dye precursor and a color developer in an organic solvent which is slightly soluble or insoluble in water, and forming the resulting solution into an emulsified dispersion, and microcapsules containing a decolorizer. The heat sensitive recording material forms a color in an unheated area from the reaction product of the dye precursor with the color developer, and the color is decolorized at a heated area by the decolorizer oozing out of the microcapsules through their thermoresponsive walls. When the heat sensitive recording material is placed on a light table, the background is viewed as colored, and the thermally recorded area is viewed as a colorless or light colored, or transparent or low-density colored image, depending on the thermal energy applied to the heat sensitive recording material.